The present invention relates to an apparatus that fabricates semiconductor devices through etching processing and more particularly to a semiconductor fabricating apparatus that has a function of determining the etching processing state such as an etched depth.
Dry-etching has been widely used in the semiconductor device formation process to remove layers of various materials, such as dielectric materials and insulating materials, formed on the surface of a semiconductor wafer or to form patterns on those layers. In the dry-etching process, it is important to adjust etching during the processing of the layers so that an etched depth desired for a layer may be obtained or so that a thin film desired for a layer may be obtained. Therefore, it is required to accurately detect the end points of etching process and the film thickness.
When dry-etching a semiconductor wafer using plasma, it is known that the light emission intensity of a specific-wavelength light included in a plasma light changes with the progress of the etching process of a specific layer. One of known technologies for checking the etching states, such as the end point of etching process and the film thickness on a semiconductor wafer, takes advantage of this characteristics to detect a change in the light emission intensity of a specific-wavelength light included in the plasma light during the dry-etching process and, based on this checking result, detects the end point of etching process on a specific layer and the film thickness of the layer. To increase detection precision, a misdetection caused by a fluctuation in the detected waveform generated by noises should be reduced.
Recently, as the wiring pitch of a semiconductor becomes finer and its density becomes higher, the open area ratio (non-etched area on a semiconductor wafer) becomes lower. This decreases the light emission intensity of a specific-wavelength light sent from the light sensor to the light detector. As a result, the level of the sampling signal from the light detector becomes lower, making it difficult for the end point determination unit to correctly detect the end point of etching process based on the sampling signal from the light detector.
When stopping processing upon detection of the end point of etching process, it is important that the thickness of the remaining dielectric layer should be equal to a predetermined value. In the conventional process, the time thickness control method is used to monitor the whole process on the assumption that the etching speed of each layer is constant. An etching speed is obtained, for example, by processing a sample wafer in advance. In this method, the etching process stops at the same time the elapsed time measured by the time monitor method becomes equal to the time corresponding to a predetermined film thickness (remaining film thickness in etching process).
However, it is known that the thickness of an actual film, for example, an SiO2 layer formed by the LPCVD (Low Pressure Chemical Vapor Deposition) method, varies from time to time. An allowable thickness error caused by a process fluctuation during LPCVD corresponds to about 10% of the initial thickness of the SiO2 layer. This means that the actual final thickness of the remaining SiO2 layer on the silicon substrate cannot be measured accurately by the time monitor method. The actual thickness of the remaining layer is measured finally by the standard emission spectroscopy. If excess etching is found, the wafer is rejected and discarded.
A technology for detecting the end point of etching process on a semiconductor wafer by measuring the surface of a wafer with the use of an interferometer is known. This technology is disclosed, for example, in JP-A-5-179467 (document 1), U.S. Pat. No. 5,658,418 (document 2), JP-A-2000-97648 (document 3), and JP-A-2000-106356 (document 4).
JP-A-5-179467 (document 1) discloses a method for detecting the end point of etching process by detecting an interference light (plasma light) using three color filters (red, green, blue). U.S. Pat. No. 5,658,418 (document 2) discloses a method for counting the extreme values (maximum and minimum of waveform: zero-pass point of differential waveform) of an interference waveform using a change in the interference waveform of two wavelengths with respect to time and its differential waveform. The etching speed is calculated by measuring the time required until the count reaches a predetermined value, the remaining etching time required until a predetermined film thickness is attained is calculated based on the calculated etching speed, and, based on the calculated time, the etching process is stopped.
JP-A-2000-97648 (document 3) discloses a method that obtains a difference waveform (that uses a wavelength as a parameter) between a light intensity pattern (that uses a wavelength as a parameter) of an interference light before processing and a light intensity pattern of the interference light after or during processing and compares the obtained waveform with the difference waveform read from the database for measuring a difference in level (film thickness). JP-A-2000-106356 (document 4), which relates to a rotary coating apparatus, discloses a method for finding the film thickness by measuring a change in the interference light of multiple wavelengths with respect to time.
When stopping processing upon detection of the end point of etching process, it is important that the thickness of the remaining film layer is close to a predetermined value as much as possible. The conventional technology monitors the film thickness by adjusting the time on the assumption that the etching speed of each layer is constant. The reference etching speed value is obtained, for example, by processing a sample wafer in advance. According to this technology, the etching process stops when the time corresponding to the predetermined film thickness elapses.